For mobile electronics, thin-and-lightweight are prime design goals, but solar cells have aimed instead at the highest efficiency. Today, making solar cells thinner and lighter would be welcome for applications in aviation, space exploration, and in remote areas where transportation costs are high, according to MIT. In the future, as materials become more scarce, the conservation achieved with ultra-thin solar cells could cost-reduce even urban installations.

"Our predictions are for what may very well be the thinnest solar cells possible, ones out of only two layers of materials," professor Jeffrey Grossman told EE Times. Grossman performed the work with post-doctorate researcher Marco Bernardi and Maurizia Palummo, a visiting researcher from the University of Rome.

"There are indeed applications where weight is crucial, where the thinnest possible amount of active layer material with minimal encapsulation may change the installation game, because it could get us onto [thinner, more durable] substrates," Grossman said. "In addition, this gets to the heart of what I think is an important question: namely, what is the most power we can squeeze out of each and every atom or bond of a given material?"

MIT researchers use computer simulations to shuffle through different materials in the search for the thinnest possible solar cells. (Source: MIT)

MIT estimates that its ultra-thin solar cell films -- essentially two-dimensional (2D) layers as thin as one nanometer -- can deliver 1,000 times more energy-per-pound than conventional solar cells. The tradeoff is that their efficiency is lower, requiring about 10 times the area of a conventional solar cell to produce the same amount of energy, since ultra-thin solar cells have an efficiency of up to 2 percent, compared with up to 20 percent for conventional photovoltaic (PV) solar cells. However, the researchers have plans for stacking the ultra-thin 2D solar cells in layered structures to improve their efficiency.

"These two-sheet stacks we predict could have efficiencies of 1 to 2 percent. However, it is certainly possible to make stacks that consist of more than just two layers, and in that case the efficiency would go up," said Grossman. "There is no reason efficiencies of cells made from 2D materials couldn't be just as efficient as current 'traditional' PV -- in the 10 to 20 percent range."

The ultra-thin solar cell design is still in simulation while the researchers decide which material to use for prototypes. In detailed simulations, various topologies of stacked sheets use atomically thin graphene, molybdenum-disulfide, and molybdenum-diselenide. The best of these designs not only provide a weight advantage over conventional solar cells, but are also immune to oxygen, ultraviolet radiation, and moisture in the environment -- the three killers of long-term stability in conventional solar cells -- giving the new ultra-thin designs the additional advantage of eliminating the need for glass covers or standoff mounting, which consumes over half the cost of conventional PV installations.

"Ultralight solar cells (with extremely high power/weight in our case) have the potential to reduce installation costs. Current solar modules based on silicon are heavy and made heavier by the glass protecting them. Their installation amounts to 60 percent of the total cost of a solar array, largely due to the high weight," said Bernardi. "By finding ultra-thin and mechanically flexible materials, the hope is to make very light solar cells, which can be encapsulated with plastics rather than glass, and hence create new paradigms for photovoltaic installation."

The material cost for ultra-thin solar cells would be minimal, compared to conventional solar cells, but the researchers have yet to create prototypes in the lab or to work on making the materials manufacturable in high volume. Next they plan to test their formulations in the lab by measuring the efficiency and long-term stability of various formulations and stacking structures.

I agree and would add that only 50 percent of the cost of PV installations is in solar cells themselves--the other 50 percent is in the mounts, stand-offs, glass coverings and such. Since thinner solar cells are lighter and more durable, then there should also be cost savings from their easier installation.

The cost of the materials is likely to be the smallest component of the total cost. Photovoltaics are semi-conductor electronics, and the cells are actually made by a wafer fab. Wafer fabs are enormously expensive, and the single biggest part of the cost of the cells will be an allocated share of the cost to build the factory that makes them.

And that's just the cost of the cells. The cells must be incorporated in an installation, and someone will have to build and install the panels.

The key here is what this potential new approach will allow in terms of application, whether it might allow applications that aren't currently possible, and whether it might be better in some existing applications.

This is interesting and promising, but there's a long way between theory and proof of concept, and an even longer way between proof of concept and volume manufacture.

No this is just under simulation and modeling phase, the actual manufacturing cost calculation will not be possible at present. But it will surely lead to all the new manufacturing techniuqe being introduced as all the materials being discussed here are not being used in the present day solar panel manufacturing.

Yes you are right that organic solar cells are already being developed for deposition on thin, ultra-cheap substrates like paper. These researchers claim that their materials are better than organic in terms of longevity, since they do not deteriorate in the presense of UV, moisture and oxygen. Also this work is aimed at testing the limits of "limbo" science--how low (thin) can you go!

Yes, the whole world is on the side of "cheaper is better than thinner," but there are applications--like spacecraft--where thinner/lighter is worth the extra money. And as is often the case, aerospace technologies get cheaper as they become more popular, so thinner might just meet cheaper down the road :)

Looks different, but I was thinking that the idea of printing solar cell on paper as it is mentioned in the link above was good except the low efficiency number of 1%. In this case also, the efficiency number 1-2% is not very encouraging...isn't it?

There are other ways to get thin without lower efficiency eg using proton implant shearing techniques rather than diamond saws. If the efficiency is much lower than 20% then the market won't be there in many cases - the limiting factor is how much area you have for deployment (eg you roof at home). In addition other elements of the system scale with area and hence the cost goes up - if this is only a few atoms thick it will need to be bonded to some thicker substrate to give it strength so that it can last through installation and long term use in the elements!

Which would do more for society, an expensive thin solar cell or a fat cheap one? I understand that one drives the other, but right now I'd rather seem the emphasis on driving high-volume use of solar everywhere as very, very low prices.

You are right. The researhers also point out that because their material does not need to be protected from UV, moisture and oxygen that the installations will also use less material for off-sets, covering and such.